Nigrostriatal pathology with reduced astrocytes in LRRK2 S910/S935 phosphorylation deficient knockin mice

Leucine-rich repeat kinase 2 (LRRK2) is genetically implicated in both familial and sporadic Parkinson's disease (PD). Moreover, LRRK2 has emerged as a compelling therapeutic target for the treatment of PD. Consequently, there is much interest in understanding LRRK2 and its role in PD pathogenesis. LRRK2 is constitutively phosphorylated on two serines, S910 and S935, that are required for interaction of LRRK2 with members of the 14-3-3 family of scaffolding proteins. Pathogenic LRRK2 missense mutations impair the phosphorylation of LRRK2 at these sites, but whether this contributes to PD pathology is unclear. To better understand how loss of LRRK2 phosphorylation relates to PD pathology, we have studied double knockin mice in which Lrrk2's serine 910 and 935 have both been mutated to alanine and can therefore no longer be phosphorylated. Nigrostriatal PD pathology was assessed in adult mice, aged mice, and mice inoculated with α-synuclein fibrils. Under all paradigms there was evidence of early PD pathology in the striatum of the knockin mice, namely alterations in dopamine regulating proteins and accumulation of α-synuclein. Striatal pathology was accompanied by a significant decrease in the number of astrocytes in the knockin mice. Despite striatal pathology, there was no degeneration of dopamine neurons in the substantia nigra and no evidence of a PD motor phenotype in the knockin mice. Our results suggest that modulation of LRRK2 serine 910 and 935 phosphorylation sites may have implications for dopamine turnover and astrocyte function, but loss of phosphorylation at these residues is not sufficient to induce PD neurodegeneration.